1. Field of the Invention
The invention relates to a method and a device for sealing a tap hole in metallurgical containers.
2. Description of the Related Art
The invention relates to a method and a device for sealing a tap hole in metallurgical containers.
Recently, there has been a tendency to produce steels of a high degree of purity, so-called clean steel, in order to thus fulfill the increasing requirements for improved steel properties. The separation of molten mass and slag in the electric furnace or converter with subsequent secondary metallurgy is an essential influencing factor with respect to the degree of purity.
From the prior art several tapping systems are known. In a conventional electric arc furnace tapping is carried out, for example, by lateral tilting of the furnace vessel. The furnace is tilted toward the tapping side for tapping, and the outflow of the molten mass is terminated by a fast return tilting after reaching the desired tapping weight. In this connection, it cannot be avoided that slag flows partially with the stream of the molten mass out of the tap hole.
After termination of tapping and the return tilting movement, the tap opening is prepared for a new batch in that the opening is closed by a closure plate and sand is filled into the opening. The sand filling process is carried out either manually or by an automated conveying system. An optimal filling of the opening with sand is not possible for a manual filling process. Moreover, this step, in the case that cleaning work has to be carried out, is time-consuming and labor-intensive.
Moreover, the slag-poor tapping system for a converter is known in connection with a float or slag stopper. In this context, a float whose specific weight is between that of the molten mass of steel and of the slag is introduced into the molten bath above the eddy caused by the outflowing molten mass. The float is lowered together with the outflowing molten mass of steel and closes the tap opening. A disadvantage is, however, that the sealing of the tap opening depends only on the lowered molten mass/slag interface and cannot be influenced otherwise. Moreover, a completely slag-free outflowing of the molten mass is not possible with this float solution.
For tapping in ladles, the so-called AMEPA system is known. This system is primarily employed for controlling the tapping from the ladle into the distributor of a continuous casting device. This is a tapping system according to the electromagnetic principal. The termination of tapping and the separation between molten mass and slag are achieved by a sensor which is mounted within the outflow of the ladle outlet. A slide system is provided which closes off the tap opening after it has been determined that slag also flows out. A slag-free tapping is not possible by this solution because the sensor reacts only after a portion of the slag has already flown through the opening.
Moreover, a pneumatic tapping system is known in the prior art which closes the metallurgical container from the exterior. However, this entails a great splashing risk.
From German patent DE 33 27 671 a device for a substantially slag-free tapping of the molten mass of metal, in particular, of molten mass of steel, from metallurgical containers is also known. This document concerns primarily the object of preventing turbulence generation during an immersion process of a closing member and thus a mixing of the slag and the molten mass. For this purpose, a closing member is suggested which can be moved by means of a liftable and lowerable rod via a lifting system into the metallurgical container. The lowering of the flow member and its securing shortly above the bottom of the container above the tap opening results in a better binding of the negative potential turbulences. It is described that the type of flow member for reducing turbulence can also be completely lowered into the tap opening at the container bottom in order to thus terminate the tapping. However, when doing so, the flow member is not completely received by the tap opening but is seated on the opening. In all of the aforementioned tapping methods of the prior art only a slag-poor, but not a slag-free, tapping is possible. This means, inter alia, that the oxygen contents in the molten mass is increased by the entrained oxide slag which entails an increased deoxidation. The oxygen contents of the FeO in the slag makes the desulfurization and degassing more difficult.
Finally, from EP 0 315 311 B1 a plug for closing the tap opening in metallurgical containers is known. This plug is comprised of a cylindrically shaped container of metal which at its ends is provided with two plates. The end which is facing into the interior of the container for mounting of the container and the corresponding inner plate are arranged so as to be spaced by a gap relative to one another. The metallic container receives refractory material such as, for example, sand. This sand is enclosed by a plastic foil. The plug is provided with a plunger with which, after placing the plug into the tap hole, it is achieved that the outer plate is moved against the inner plate along a linkage which penetrates the sand mass. Accordingly, the plastic foil is torn. This process is enhanced by an edge area of the container provided with teeth. The sand exits from the gap and flows into the intermediate space between container and outflow opening and thus provides a sealing connection. Subsequently, the plunger is removed while the metallic container remains within the tap hole.
The present invention has accordingly the object to provide a method and a tapping system with which in a simple and inexpensive way a slag-free tapping of a metallurgical container can be performed so that steels of a high degree of purity can be produced.
This object is solved according to the invention in regard to the method by controlling the time of introduction of the plug which comprises a plug sleeve as well as a core of a refractory flowable material, closing off the tap opening from the exterior of the container, and changing the consistency and/or shape of the plug sleeve by temperature action such that the flowable material is distributed in the tap opening in a sealing fashion and in regard to the device in that the plug comprises a plug sleeve fitting the tab opening as well as a core of a refractory flowable material, that the plug sleeve itself is comprised of a material which is resistant relative to the molten mass of metal only for a short period of time with respect to its consistency and/or shape.
The core of the invention is the provision of a tapping plug system with which the tap opening of a metallurgical container can be optimally sealed. This is achieved according to the invention by a special configuration of the plug. According to the method of the invention it is suggested to control the time of introduction of the plug into the tap opening, for example, as a function of the weight of the tapped steel, of the bath level, or by means of a slag detection system. Preferably, automatic but also semiautomatic or manual controls are possible. The time of introduction can be controlled point-by-point or, for example, by means of a signal which is determined by means of visual sensing or by means of a monitor indicator.
The present invention has accordingly the object to provide a method and a tapping system with which in a simple and inexpensive way a slag-free tapping of a metallurgical container can be performed so that steels of a high degree of purity can be produced.
This object is solved according to the invention in regard to the method by controlling the time of introduction of the plug which comprises a plug sleeve as well as a core of a refractory flowable material, closing off the tap opening from the exterior of the container, and changing the consistency and/or shape of the plug sleeve by temperature action such that the flowable material is distributed in the tap opening in a sealing fashion and in regard to the device in that the plug comprises a plug sleeve fitting the tab opening as well as a core of a refractory flowable material, that the plug sleeve itself is comprised of a material which is resistant relative to the molten mass of metal only for a short period of time with respect to its consistency and/or shape.
The plug according to the invention is comprised of a plug sleeve which receives a flowable material. This filled plug sleeve is introduced into the tap opening through the liquid metal or from the exterior of the metallurgical container. Subsequently, the tap opening is closed, for example, by means of the closure plate. The invention takes advantage of the fact that the material of the plug sleeve with respect to its consistency and/or its shape is changed by temperature effects such that the flowable material can distribute itself in the tap opening in a sealing fashion. The material of the plug sleeve is preferably a heat-insulating material, for example, cardboard or wood.
The flowable material is preferably filler sand. After destruction of the sleeve, it forms at the contact surface with the molten mass of metal a sinter layer which seals the tap opening. This provides an additional sealing action. Since the amount of the filler sand in the plug sleeve can be metered and, depending on the wear of the tap hole, can also be varied, the tap hole can be sealed with an optimal amount of sand. This can thus prevent that the sand cannot fill the hole entirely for sealing. Accordingly, problems during opening of the tap hole are circumvented.
Preferably, the introduction means for the plug sleeve is a metal rod or a metal pipe which can be moved through the molten mass to the tap opening. Advantageously, the metal rod or the metal pipe is comprised of members which make it possible to move it by means of an arc-shaped guide out of a horizontal position into a vertical position.
For protecting the metal rod or the pipe against the hot molten mass, they are surrounded by a protective pipe. This protective pipe is also comprised of a material which is resistant for a short period of time relative to the molten mass of metal. Preferably, this material for the plug sleeve and the protective pipe is cardboard which will coke within the molten mass of metal. Also, all other kinds of materials are conceivable which, as a result of the temperature effect of the molten mass of metal, change their consistency, which also includes complete dissolution, or change their shape in that they lose strength.
The filler sand received in the sleeve can contain binders which are destroyed at the temperatures at the level of the molten mass of metal. Moreover, it is conceivable that the filler sand within the sleeve is surrounded by an intermediate protective layer and is vacuum-sealed. This intermediate protective layer is advantageously a foil which dissolves at the temperatures present.
Above the filler sand, a support plate is provided. By means of the support plate, the rod or the pipe can force the filler sand farther downwardly.
A further embodiment of the invention suggests that, in addition to the plug sleeve as a first chamber for receiving a filler material, the hollow space of the protective pipe is used as a second chamber. The second chamber serves as a storage chamber for filler material. The second chamber is filled with filler material especially when the diameter of the tap opening, as a result of wear, has become larger.
When the introduction means for introducing the plug up to the tap opening is a rod, this second chamber is between the rod, which can be axially guided through the protective pipe, and the inner mantle surface of the protective pipe. The amount of filler material in this second chamber can be selected depending on the need. In the case that the means for introducing is a pipe, it penetrates the first chamber with the surrounding protective pipe. The second chamber is formed in the hollow space of the introduction pipe within and above the first chamber. The two embodiments provide that the bottom of the first chamber is provided with a plug, preferably of ceramic material. As a protection of the filler material during penetration of the hot molten mass, the chambers as well as the plug are surrounded by a heat-insulating plug sleeve. This plug is movable as a result of its pressure loading by means of the rod or the pipe. As a result of the movement of the introduction means, the plug is displaced, the sleeve at the bottom is destroyed, and the filler material exits.
The suggested method and the plug exhibit the advantage of a slag-free tapping. When employing the method already in the electric furnace, the secondary metallurgical treatment, in particular, with respect to the current requirements of clean steel is considerably simplified. The uncontrolled aluminum melting loss by entrained slag is prevented. The invention results in savings of deoxidation agent, of the added wires such as CaSi as well as the synthetic slag. Moreover, more beneficial conditions for the desulfurization and degassing are provided. The casting properties are improved.
With the inventive method it is possible to terminate the tapping at a precisely determined nominal tapping weight. With suitable systems the time of introduction of the plug into the tap opening, for example, as a function of the weight of the already tapped molten mass, is controlled. Moreover, the point of introduction can be controlled by means of a bath level measuring system or an early detection system for slag.